Battery Separators with Controlled Pore Structure

ABSTRACT

Disclosed are battery separators comprising glass fibers and having a basis weight (gsm), a specific surface area (m 2 /g), a density (gsm/mm) and a mean pore size (μm), which satisfy the equation disclosed herein, provided that: the specific surface area is less than 1.5 m 2 /g, or the density is greater than 180 gsm/mm. Also disclosed are batteries comprising the battery separators, and processes for making the separators.

BACKGROUND

Batteries are commonly used as energy sources. Typically, a batteryincludes a negative electrode and a positive electrode. The negative andpositive electrodes are often disposed in an electrolytic medium. Duringdischarge of a battery, chemical reactions occur wherein an activepositive electrode material is reduced and active negative electrodematerial is oxidized. During the reactions, electrons flow from thenegative electrode to the positive electrode through a load, and ions inthe electrolytic medium flow between the electrodes. To prevent directreaction of the active positive electrode material and the activenegative electrode material, the electrodes are mechanically andelectrically isolated from each other by a separator.

One type of battery is a lead-acid battery. In a lead acid battery, leadis usually an active negative electrode material, and lead dioxide isusually an active positive electrode material. (In a lead-acid battery,the electrodes are often referred to as “plates”.) Generally, lead acidbatteries also contain sulfuric acid, which serves as an electrolyte andparticipates in the chemical reactions.

A mat comprised of glass fibers may serve as a separator. The glass matseparator has a critical role in electrolyte filling. Changes in thephysical properties of this material may have an impact on the qualityof the filled and formed battery. The separator structure, including itsfiber composition, may influence how well an unfilled element willaccept electrolyte, sustainment of pressure or force on the internalcell components, as well as certain attributes of battery performance.

When electrolyte is added to the battery, the ideal situation is thatall areas are wetted as much as possible by the same amount andconcentration of acid so that there is perfectly uniform distribution ofelectrolyte throughout the plate stack when the filling process iscompleted. This ideal situation is difficult or impossible to achieve inpractice, as there is a dynamic competition between the separator andthe plate surfaces for the electrolyte. As the electrolyte penetratesinto the plate stack, it is held up by the separator (the capillaryforces tend to hold the electrolyte rather strongly), and at the sametime the electrolyte is depleted by the exothermic reaction of thesulfuric acid with the plate by the simple chemical reaction ofPbO+H₂SO₄=>PbSO₄+H₂O. As the liquid front penetrates deeper into thestack it becomes more dilute and also gets hotter, due to the exothermicreaction with the lead oxide. As the acid reacts with the lead oxide,the sulfuric acid electrolyte becomes progressively more dilute. Leadsulfate is relatively soluble in the hot electrolyte with low acidstrength and near neutral pH, and dissolved lead sulfate will diffuseinto the separator. This will hasten the formation of lead dendrites inthe separator and/or hydration shorts. A short circuit may develop andbe detected during formation, or more subtly the battery will failprematurely in service due to the formation of lead dendritespenetrating the structure and short circuiting the positive and negativeplates. If the filling process is poor or incomplete, individual cellsmay also have “dry areas” after filling. These poorly wetted areas mayinclude no acid or water (completely dry), dilute acid or just water.These dry areas will slowly become wetted during and after formation,but significant grid corrosion may result due to unformed activematerial forcing all of the current to flow through the grid only.

During discharge, the sulfuric acid in the electrolyte is consumed andwater is produced, diluting the acid concentration and causing thespecific gravity of the electrolyte to decrease. During charging,formation of lead and lead dioxide in the negative and positive plates,respectively, results in release of pure sulfuric acid. Due to its highspecific gravity, the pure sulfuric acid tends to settle toward thebottom (or “stratify”, creating layers) in the electrolyte, a phenomenonknown as “acid stratification”. In a stratified battery, electrolyteconcentrates at the bottom, starving the upper part of the cell. Thelight acid on top limits plate activation, promotes corrosion andreduces the performance, while the high acid concentration on the bottomcreates heavy sulfation and large crystals reducing battery performance.

Unfortunately, design or materials changes that improve certainperformance attributes can negatively affect other performanceattributes and/or increase cost.

SUMMARY

There is a need for a battery separator that can balance certainperformance attributes while not significantly negatively affectingother performance attributes and/or increasing cost. For example,coarser fibers (i.e., having a larger average diameter) are generallyless expensive than finer fibers (i.e., having a smaller averagediameter), and some coarser fibers impart a desirable compressionstrength to the separator. The design of any battery involves thebalancing of a number of different properties, and results in a need fora separator having certain attributes, such as a particular mean poresize or wet tensile strength. Separators made from coarser fibersgenerally exhibit lower wet tensile strength and generally have a largermean pore size than those made from finer fibers, all other factorsbeing equal. Accordingly, a separator requiring certain characteristicssuch as a smaller mean pore size and/or higher wet tensile strength maydemand the use of more expensive finer fibers.

In one aspect, the invention encompasses the insight that by controllingthe density, a separator having certain attributes such as mean poresize and wet tensile strength can be achieved using a higher percentageof coarser fibers than was previously possible. In some embodiments, thedensity of the separator is controlled by employing densification in theprocess of making the separator.

In one aspect, the invention relates to a battery separator comprisingglass fibers and having a basis weight (gsm), a specific surface area(m²/g), a density (gsm/mm) and a mean pore size (μm), wherein thefollowing equation (“eq. 1”) is satisfied (when the quantities have theindicated units):

${{mean}\mspace{14mu} {pore}\mspace{14mu} {size}} < {\left( \frac{270}{{basis}\mspace{14mu} {weight}} \right)^{0.53}*\frac{1.6}{{specific}\mspace{14mu} {surface}\mspace{14mu} {area}}*\left( {\frac{65}{\sqrt{density}} - 1.8} \right)}$

provided that:

-   -   the specific surface area is less than 1.5 m²/g, or    -   the density is greater than 180 gsm/mm.        It should be appreciated that eq. 1 is a relational equation,        i.e., provided that the quantities inputted have the indicated        units, as long as the numerical value of the right-hand side of        the equation as written is greater than the left-hand side, the        equation is satisfied. For example, if the numerical value of        the right-hand side is 4.0, and the the numerical value of the        left-hand side is 3.5, then the equation is satisfied inasmuch        as 3.5<4.0.

In one aspect, the invention relates to a battery separator comprisingglass fibers and having a basis weight (gsm), a specific surface area(m²/g), a density (gsm/mm) and a mean pore size (μm), wherein eq. 1 issatisfied (when the quantities have the indicated units); provided that:the specific surface area is less than 1.5 m²/g, or the density isgreater than 180 gsm/mm; wherein the separator is produced by a processdescribed herein.

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and a battery separator disposedbetween the negative and positive plates; wherein the battery separatorcomprises glass fibers and has a basis weight (gsm), a specific surfacearea (m²/g), a density (gsm/mm) and a mean pore size (μm), wherein eq. 1is satisfied (when the quantities have the indicated units); providedthat: the specific surface area is less than 1.5 m²/g, or the density isgreater than 180 gsm/mm.

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and a battery separator disposedbetween the negative and positive plates; wherein the battery separatorcomprises glass fibers and has a basis weight (gsm), a specific surfacearea (m²/g), a density (gsm/mm) and a mean pore size (μm), wherein eq. 1is satisfied (when the quantities have the indicated units); providedthat: the specific surface area is less than 1.5 m²/g, or the density isgreater than 180 gsm/mm; wherein the separator is produced by a processdescribed herein.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an apparatus for use with the procedure described inExample 2.3: measurement of vacuum fill (acid filling) time.

FIG. 2 shows a compression/recovery graph as described in Example 2.5.

FIG. 3 shows an apparatus for use with the procedure described inExample 2.4: measurement of acid stratification distance.

FIG. 4 illustrates the relationship between acid fill time and the ratioof specific surface area of pasting paper to separator as describedherein.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS Definitions

Unless otherwise specified, when a value is stated to be “between” twoendpoints or “from” one endpoint to another endpoint, the endpoints areintended to be included. For example, a value “between 2 and 20” or“from 2 to 20” includes both 2 and 20 as well as the values between.

Unless otherwise specified, the terms “include”, “includes”,“including”, etc. are intended to be open-ended. That is, “including Aand B” means including but not limited to A and B.

Amounts indicated as “% (w/w)” refer to percentage by weight.

Values of specific gravity are given with water at 4° C. as thereference.

Composition

In one aspect, the invention relates to a battery separator comprisingglass fibers and having a basis weight (gsm), a specific surface area(m²/g), a density (gsm/mm) and a mean pore size (μm), wherein thefollowing equation (“eq. 1”) is satisfied (when the quantities have theindicated units):

${{mean}\mspace{14mu} {pore}\mspace{14mu} {size}} < {\left( \frac{270}{{basis}\mspace{14mu} {weight}} \right)^{0.53}*\frac{1.6}{{specific}\mspace{14mu} {surface}\mspace{14mu} {area}}*\left( {\frac{65}{\sqrt{density}} - 1.8} \right)}$

provided that:

the specific surface area is less than 1.5 m²/g, or

the density is greater than 180 gsm/mm.

In some embodiments, the specific surface area of the separator is lessthan 1.5 m²/g. In some embodiments, the density of the separator isgreater than 180 gsm/mm.

In some embodiments, the separator comprises or is a part of a non-wovenfiber web.

Fine Fibers

As used herein, “fine fibers” are fibers having an average diameter lessthan or equal to 1.0 μm. In some embodiments, the separator comprisesfrom about 5% to about 50% (w/w) fine fibers. In some embodiments, theseparator comprises from about 5% to about 45% (w/w) fine fibers. Insome embodiments, the separator comprises from about 5% to about 40%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 5% to about 35% (w/w) fine fibers. In some embodiments, theseparator comprises from about 5% to about 30% (w/w) fine fibers. Insome embodiments, the separator comprises from about 5% to about 25%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 5% to about 20% (w/w) fine fibers. In some embodiments, theseparator comprises from about 5% to about 15% (w/w) fine fibers.

In some embodiments, the separator comprises from about 10% to about 50%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 15% to about 50% (w/w) fine fibers. In some embodiments, theseparator comprises from about 20% to about 50% (w/w) fine fibers. Insome embodiments, the separator comprises from about 25% to about 50%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 30% to about 50% (w/w) fine fibers. In some embodiments, theseparator comprises from about 35% to about 50% (w/w) fine fibers. Insome embodiments, the separator comprises from about 40% to about 50%(w/w) fine fibers.

In some embodiments, the separator comprises from about 10% to about 45%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 10% to about 40% (w/w) fine fibers. In some embodiments, theseparator comprises from about 15% to about 45% (w/w) fine fibers. Insome embodiments, the separator comprises from about 15% to about 40%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 15% to about 35% (w/w) fine fibers. In some embodiments, theseparator comprises from about 20% to about 40% (w/w) fine fibers. Insome embodiments, the separator comprises from about 20% to about 35%(w/w) fine fibers. In some embodiments, the separator comprises fromabout 20% to about 30% (w/w) fine fibers. In some embodiments, theseparator comprises from about 25% to about 35% (w/w) fine fibers.

In some embodiments, the fine fibers of the separator have an averagediameter from about 0.05 to 1.0 μm. In some embodiments, the fine fibersof the separator have an average diameter from about 0.05 to about 0.9μm. In some embodiments, the fine fibers of the separator have anaverage diameter from about 0.05 to about 0.8 μm. In some embodiments,the fine fibers of the separator have an average diameter from about0.05 to about 0.7 μm. In some embodiments, the fine fibers of theseparator have an average diameter from about 0.05 to about 0.6 μm. Insome embodiments, the fine fibers of the separator have an averagediameter from about 0.05 to about 0.5 μm. In some embodiments, the finefibers of the separator have an average diameter from about 0.2 to 1.0μm. In some embodiments, the fine fibers of the separator have anaverage diameter from about 0.3 to 1.0 μm. In some embodiments, the finefibers of the separator have an average diameter from about 0.4 to 1.0μm. In some embodiments, the fine fibers of the separator have anaverage diameter from about 0.5 to 1.0 μm. In some embodiments, the finefibers of the separator have an average diameter from about 0.6 to 1.0μm. In some embodiments, the fine fibers of the separator have anaverage diameter from about 0.2 to about 0.8 μm. In some embodiments,the fine fibers of the separator have an average diameter from about 0.3to about 0.7 μm. In some embodiments, the fine fibers of the separatorhave an average diameter of less than or equal to 0.9 μm. In someembodiments, the fine fibers of the separator have an average diameterof less than or equal to 0.8 μm. In some embodiments, the fine fibers ofthe separator have an average diameter of less than or equal to 0.7 μm.In some embodiments, the fine fibers of the separator have an averagediameter of less than or equal to 0.6 μm. In some embodiments, the finefibers of the separator have an average diameter of less than or equalto 0.5 μm. In some embodiments, the fine fibers of the separator have anaverage diameter of less than or equal to 0.4 μm. In some embodiments,the fine fibers of the separator have an average diameter of less thanor equal to 0.3 μm. In some embodiments, the fine fibers of theseparator have an average diameter of less than or equal to 0.2 μm.

In some embodiments, the fine fibers of the separator are at least 5%(w/w), at least 10% (w/w), at least 15% (w/w), at least 20% (w/w), atleast 25% (w/w), at least 30% (w/w), at least 35% (w/w), at least 40%(w/w), at least 45% (w/w), at least 50% (w/w), at least 55% (w/w), atleast 60% (w/w), at least 65% (w/w), at least 70% (w/w), at least 75%(w/w), at least 80% (w/w), at least 85% (w/w), at least 90% (w/w), atleast 95% (w/w), or about 100% glass fibers.

Coarse Fibers

As used herein, “coarse fibers” are fibers having an average diametergreater than 1.0 μm. In some embodiments, the separator comprises fromabout 50% to about 95% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 50% to about 90% (w/w) coarse fibers. Insome embodiments, the separator comprises from about 50% to about 85%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 50% to about 80% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 50% to about 75% (w/w) coarse fibers. Insome embodiments, the separator comprises from about 50% to about 70%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 50% to about 65% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 50% to about 60% (w/w) coarse fibers.

In some embodiments, the separator comprises from about 55% to about 95%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 60% to about 95% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 65% to about 95% (w/w) coarse fibers. Insome embodiments, the separator comprises from about 70% to about 95%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 75% to about 95% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 80% to about 95% (w/w) coarse fibers. Insome embodiments, the separator comprises from about 85% to about 95%(w/w) coarse fibers.

In some embodiments, the separator comprises from about 55% to about 90%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 55% to about 85% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 60% to about 90% (w/w) coarse fibers. Insome embodiments, the separator comprises from about 60% to about 85%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 60% to about 80% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 65% to about 85% (w/w) coarse fibers. Insome embodiments, the separator comprises from about 65% to about 80%(w/w) coarse fibers. In some embodiments, the separator comprises fromabout 65% to about 75% (w/w) coarse fibers. In some embodiments, theseparator comprises from about 70% to about 80% (w/w) coarse fibers.

In some embodiments, the coarse fibers of the separator have an averagediameter of greater than or equal to 1.2 μm. In some embodiments, thecoarse fibers of the separator have an average diameter from about 1.2to about 50 μm. In some embodiments, the coarse fibers of the separatorhave an average diameter from about 1.2 to about 20 μm. In someembodiments, the coarse fibers of the separator have an average diameterfrom about 1.2 to about 15 μm. In some embodiments, the coarse fibers ofthe separator have an average diameter from about 1.2 to about 10 μm. Insome embodiments, the coarse fibers of the separator have an averagediameter from about 1.2 to about 7 μm. In some embodiments, the coarsefibers of the separator have an average diameter from about 1.2 to about5 μm. In some embodiments, the coarse fibers of the separator have anaverage diameter from about 1.2 to about 4 μm. In some embodiments, thecoarse fibers of the separator have an average diameter from about 1.2to about 3 μm. In some embodiments, the coarse fibers of the separatorhave an average diameter from about 3 to about 20 μm. In someembodiments, the coarse fibers of the separator have an average diameterfrom about 3 to about 18 μm. In some embodiments, the coarse fibers ofthe separator have an average diameter from about 5 to about 15 μm. Insome embodiments, the coarse fibers of the separator have an averagediameter from about 7 to about 15 μm. In some embodiments, the coarsefibers of the separator have an average diameter from about 3 to about12 μm. In some embodiments, the coarse fibers of the separator have anaverage diameter from about 5 to about 12 μm. In some embodiments, thecoarse fibers of the separator have an average diameter from about 7 toabout 12 μm. In some embodiments, the coarse fibers of the separatorhave an average diameter from about 5 to about 10 μm. In someembodiments, the coarse fibers of the separator have an average diameterfrom about 7 to about 9 μm. In some embodiments, the coarse fibers ofthe separator have an average diameter of greater than or equal to 2 μm.In some embodiments, the coarse fibers of the separator have an averagediameter of greater than or equal to 3 μm. In some embodiments, thecoarse fibers of the separator have an average diameter of greater thanor equal to 5 μm. In some embodiments, the coarse fibers of theseparator have an average diameter of greater than or equal to 7 μm.

In some embodiments, the coarse fibers of the separator are at least 5%(w/w), at least 10% (w/w), at least 15% (w/w), at least 20% (w/w), atleast 25% (w/w), at least 30% (w/w), at least 35% (w/w), at least 40%(w/w), at least 45% (w/w), at least 50% (w/w), at least 55% (w/w), atleast 60% (w/w), at least 65% (w/w), at least 70% (w/w), at least 75%(w/w), at least 80% (w/w), at least 85% (w/w), at least 90% (w/w), atleast 95% (w/w), or about 100% glass fibers.

In some embodiments, the separator comprises polymeric fibers. In someembodiments, the coarse fibers of the separator are at least 5% (w/w),at least 10% (w/w), at least 15% (w/w), at least 20% (w/w), at least 25%(w/w), at least 30% (w/w), at least 35% (w/w) or at least 40% (w/w)polymeric fibers. The polymeric fibers may be in the form of staplefibers and/or synthetic pulp, and may be melted or partially melted, ormay form a scrim.

Glass Fibers

In some embodiments, the glass fibers include microglass fibers, choppedstrand glass fibers, or a combination thereof. Microglass fibers andchopped strand glass fibers are known to those skilled in the art. Oneskilled in the art is able to determine whether a glass fiber ismicroglass or chopped strand by observation (e.g., optical microscopy,electron microscopy). The terms refer to the technique(s) used tomanufacture the glass fibers. Such techniques impart the glass fiberswith certain characteristics. In general, chopped strand glass fibersare drawn from bushing tips and cut into fibers in a process similar totextile production. Chopped strand glass fibers are produced in a morecontrolled manner than microglass fibers, and as a result, choppedstrand glass fibers will generally have less variation in fiber diameterand length than microglass fibers. Microglass fibers are drawn frombushing tips and further subjected to flame blowing or rotary spinningprocesses. In some cases, fine microglass fibers may be made using aremelting process. In this respect, microglass fibers may be fine orcoarse.

Microglass fibers may also have chemical differences from chopped strandglass fibers. In some cases, though not required, chopped strand glassfibers may contain a greater content of calcium or sodium thanmicroglass fibers. For example, chopped strand glass fibers may be closeto alkali free with high calcium oxide and alumina content. Microglassfibers may contain 10-15% alkali (e.g., sodium, magnesium oxides) andhave relatively lower melting and processing temperatures.

The microglass fibers can have small diameters such as less than 10.0μm. For example, the average diameter of the microglass fibers in theseparator—as opposed to the average diameter of all the glass fibers inthe separator—can be between 0.1 μm to about 9.0 μm; and, in someembodiments, between about 0.3 μm and about 6.5 μm, or between about 1.0μm and 5.0 μm. In certain embodiments, the microglass fibers can have anaverage fiber diameter of less than about 7.0 μm, less than about 5.0μm, less than about 3.0 μm, or less than about 1.0 μm. In certainembodiments, the microglass fibers can be subjected to a rotary spinningprocess and have an average fiber diameter of between about 0.6 andabout 10.0 μm, e.g., between about 0.8 and about 10.0 μm, between about1.0 and about 10.0 μm, between about 3.0 and about 9.0 μm, between about5.0 and about 8.0 μm, between about 6.0 and about 10.0 μm, or betweenabout 7.0 and about 9.0 μm; or about 9.5 μm, about 9.0 μm, about 8.5 μm,about 8.0 μm, about 7.5 μm, about 7.0, about 7.0 μm, about 6.5 μm, about6.0 μm, about 5.5 μm, about 5.0 μm, about 4.5 μm, about 4.0 μm, about3.5 μm, about 3.0 μm, about 2.5 μm, about 2.0 μm, or about 1.5 μm.Average diameter distributions for microglass fibers are generallylog-normal. However, it can be appreciated that microglass fibers may beprovided in any other appropriate average diameter distribution (e.g.,Gaussian distribution, a distribution with a geometric standarddeviation of twice the average diameter, etc.).

The microglass fibers can vary significantly in length as a result ofprocess variations. The aspect ratios (length to diameter ratio) of themicroglass fibers in a region can be generally in the range of about 100to 10,000. In some embodiments, the aspect ratio of the microglassfibers in a region are in the range of about 200 to 2500; or, in therange of about 300 to 600. In some embodiments, the average aspect ratioof the microglass fibers in a region may be about 1,000; or about 300.It should be appreciated that the above-noted dimensions are notlimiting and that the microglass fibers can also have other dimensions.

The chopped strand glass fibers can have an average fiber diameter thatis greater than the diameter of the microglass fibers. In someembodiments, the chopped strand glass fibers have an average diameter ofgreater than about 5 μm. For example, the average diameter range can beup to about 30 μm. In some embodiments, the chopped strand glass fiberscan have an average fiber diameter between about 5 μm and about 20 μm.In some embodiments, the chopped strand glass fibers can have an averagefiber diameter between about 8 μm and about 20 μm. In some embodiments,the chopped strand glass fibers can have an average fiber diameterbetween about 10 μm and about 18 μm. In some embodiments, the choppedstrand glass fibers can have an average fiber diameter between about 12μm and about 16 μm. In some embodiments, the chopped strand glass fiberscan have an average fiber diameter between about 5 μm and about 12 μm.In certain embodiments, the chopped strand fibers can have an averagefiber diameter of less than about 10.0 μm, less than about 8.0 μm, lessthan about 6.0 μm. Average diameter distributions for chopped strandglass fibers are generally log-normal. However, it can be appreciatedthat chopped strand glass fibers can be provided in any appropriateaverage diameter distribution. In some embodiments, chopped strand glassfibers can have an average length greater than or equal to 1 mm. Forexample, in some embodiments, chopped strand glass fibers have anaverage length from about 1 mm to about 25 mm, about 3 mm to about 24mm, about 3 mm to about 12 mm, about 3 mm to about 9 mm, about 6 mm,about 12 mm to about 24 mm, about 15 mm to about 21 mm, about 18 mm,about 3 mm to about 21 mm, about 6 mm to about 18 mm, about 9 mm toabout 15 mm, or about 12 mm.

It should be appreciated that the above-noted dimensions are notlimiting and that the microglass and/or chopped strand fibers can alsohave other dimensions.

In some embodiments, the glass fibers of the separator comprise acombination of chopped strand glass fibers and microglass fibers. Insome embodiments, the glass fibers of the separator can comprise betweenabout 0 weight percent to about 100 weight percent chopped strand glassfibers. For example, in some embodiments, the glass fibers of theseparator comprise from about 0 weight percent to about 20 weightpercent, from about 5 weight percent to about 20 weight percent, fromabout 5 weight percent to about 15 weight percent, from about 10 weightpercent to about 15 weight percent, from about 20 weight percent toabout 35 weight percent, from about 35 weight percent to about 50 weightpercent, from about 50 weight percent to about 65 weight percent, fromabout 65 weight percent to about 80 weight percent, from about 80 weightpercent to about 100 weight percent, from about 20 weight percent toabout 60 weight percent, from about 40 weight percent to about 80 weightpercent, or from about 60 weight percent to about 100 weight percentchopped strand glass fibers. In some embodiments, the glass fibers ofthe separator can comprise between about 0 weight percent to about 100weight percent microglass fibers. For example, in some embodiments, theglass fibers of the separator comprise from about 80 weight percent toabout 100 weight percent, from about 65 weight percent to about 80weight percent, from about 50 weight percent to about 65 weight percent,from about 35 weight percent to about 50 weight percent, from about 20weight percent to about 35 weight percent, from about 0 weight percentto about 20 weight percent, from about 40 weight percent to about 80weight percent, from about 20 weight percent to about 60 weight percent,or from about 0 weight percent to about 40 weight percent microglassfibers.

Other Materials

Additionally, a separator can include a variety of other materials ofconstruction. For example, the separator can include, in addition toglass fibers, non-glass fibers, natural fibers (e.g., cellulose fibers),synthetic fibers (e.g., polymeric), fibrillated fibers, binder resin,ceramic materials, solulizable fiber (e.g., polyvinyl alcohol solublebinder fiber) or any combination thereof. Additionally, the fibers caninclude thermoplastic binder fibers. Exemplary thermoplastic fibersinclude bi-component, polymer-containing fibers, such as sheath-corefibers, or side-by-side fibers. Examples of polymer fibers includepolyalkylenes (e.g., polyethylene, polypropylene, polybutylene),polyesters (e.g., polyethylene terephthalate), polyamides (e.g., nylons,aramids), halogenated polymers (e.g., polytetrafluoroethylenes), andcombinations thereof. Bicomponent fibers can be, e.g., from 0.1 to 15decitex (weight in grams of 10,000 meters of fiber); can have a fiberlength of e.g., 1-24 mm. In some embodiments, the separator containbetween about 0 weight percent to about 30 weight percent of bicomponentfibers (e.g., between about 1% and about 15%, between about 1% and about8%, between about 6% and about 8%, between about 6% and about 10%,between about 10% and about 15% or between about 10% and about 20%).

Separator Characteristics

As described above, in a separator of the invention, mean pore size(μm), the basis weight (gsm), the specific surface area (m²/g) and thedensity (gsm/mm) are related by the following equation (“eq. 1”) (whenthe quantities have the indicated units):

${{mean}\mspace{14mu} {pore}\mspace{14mu} {size}} < {\left( \frac{270}{{basis}\mspace{14mu} {weight}} \right)^{0.53}*\frac{1.6}{{specific}\mspace{14mu} {surface}\mspace{14mu} {area}}*\left( {\frac{65}{\sqrt{density}} - 1.8} \right)}$

provided that:

the specific surface area is less than 1.5 m²/g, or

the density is greater than 180 gsm/mm.

Pore Size

The mean pore size is measured according to the Battery CouncilInternational Standard BCIS-03a (Rev Sep09) method 6, “Pore SizeCharacteristics by the Liquid Porosimetry Method”.

In some embodiments, the mean pore size can be less than 6 μm. Forexample, in some embodiments, the mean pore size is about 0.5 μm toabout 5.5 μm, about 0.7 μm to about 5.3 μm or about 1.0 μm to about 5.0μm. In some embodiments in which the mean pore size is less than 6 μm,the maximum pore size is about 20 μm and the minimum pore size is about0.1 μm. In some embodiments in which the mean pore size is less than 6μm, the maximum pore size is about 17 μm and the minimum pore size isabout 0.2 μm.

In some embodiments, the mean pore size can be less than 5 μm. Forexample, in some embodiments, the mean pore size is about 1.0 μm toabout 4.5 μm, about 1.2 μm to about 4.3 μm or about 1.5 μm to about 4.0μm. In some embodiments in which the mean pore size is less than 5 μm,the maximum pore size is about 15 μm and the minimum pore size is about0.3 μm.

In some embodiments, the mean pore size can be less than 4 μm. Forexample, in some embodiments, the mean pore size is about 1.5 μm toabout 3.9 μm, about 1.7 μm to about 3.9 μm, about 1.9 μm to about 3.9 μmabout 2.1 μm to about 3.9 μm, about 2.3 μm to about 3.9 μm, about 2.5 μmto about 3.9 μm, about 1.5 μm to about 3.8 μm, about 1.5 μm to about 3.7μm, about 1.5 μm to about 3.6 μm, about 1.5 μm to about 3.5 μm, about1.7 μm to about 3.8 μm, about 1.9 μm to about 3.7 μm, about 2.1 μm toabout 3.6 μm, about 2.3 μm to about 3.5 μm, about 2.4 μm to about 3.4μm, about 2.4 μm to about 3.0 μm or about 2.7 μm to about 3.3 μm. Insome embodiments in which the mean pore size is less than 4 μm, themaximum pore size is about 13 μm and the minimum pore size is about 0.4μm.

Specific Surface Area

The specific surface area (BET) is measured according to method number 8of Battery Council International Standard BCIS-03A (Sep 2009), “BCIRecommended Test Methods VRLA-AGM Battery Separators”, method number 8being “Surface Area”. Following this technique, the BET specific surfacearea is measured via adsorption analysis using a BET surface analyzer(e.g., Micromeritics Gemini II 2370 Surface Area Analyzer) with nitrogengas; the sample amount is between 0.5 and 0.6 grams in a ¾ inch tube;and, the sample is allowed to degas at 75° C. for a minimum of 3 hours.

In some embodiments, the specific surface area of the separator is lessthan 1.5 m²/g. For example, in some embodiments the specific surfacearea of the separator is about 0.1 m²/g to less than 1.5 m²/g, about 0.2m²/g to less than 1.5 m²/g, about 0.3 m²/g to less than 1.5 m²/g, about0.4 m²/g to less than 1.5 m²/g, about 0.5 m²/g to less than 1.5 m²/g,about 0.6 m²/g to less than 1.5 m²/g, about 0.7 m²/g to less than 1.5m²/g, about 0.8 m²/g to less than 1.5 m²/g, about 0.9 m²/g to less than1.5 m²/g, about 1.0 m²/g to less than 1.5 m²/g, about 1.1 m²/g to lessthan 1.5 m²/g, about 1.2 m²/g to less than 1.5 m²/g, about 1.3 m²/g toless than 1.5 m²/g, about 1.4 m²/g to less than 1.5 m²/g, about 1.0 m²/gto about 1.45 m²/g, about 1.0 m²/g to about 1.4 m²/g, about 1.0 m²/g toabout 1.35 m²/g, about 1.0 m²/g to about 1.3 m²/g, about 1.1 m²/g toabout 1.45 m²/g, about 1.15 m²/g to about 1.45 m²/g, about 1.2 m²/g toabout 1.45 m²/g, about 1.25 m²/g to about 1.45 m²/g or about 1.3 m²/g toabout 1.45 m²/g.

In some embodiments, namely, where the density of the separator isgreater than 180 gsm/mm, the specific surface area of the separator canbe, but need not be, greater than 1.5 m²/g. For example, in someembodiments the specific surface area of the separator is about 0.2 m²/gto about 2.5 m²/g, about 0.4 m²/g to about 2.5 m²/g, about 0.6 m²/g toabout 2.5 m²/g, about 0.8 m²/g to about 2.5 m²/g, about 1.0 m²/g toabout 2.5 m²/g, about 1.1 m²/g to about 2.5 m²/g, about 1.2 m²/g toabout 2.5 m²/g, about 1.3 m²/g to about 2.5 m²/g, about 1.4 m²/g toabout 2.5 m²/g, about 1.6 m²/g to about 2.5 m²/g, about 1.8 m²/g toabout 2.5 m²/g, about 1.0 m²/g to about 2.4 m²/g, about 1.0 m²/g toabout 2.2 m²/g, about 1.0 m²/g to about 2.0 m²/g, about 1.0 m²/g toabout 1.8 m²/g, about 1.0 m²/g to about 1.6 m²/g, about 1.1 m²/g toabout 2.4 m²/g, about 1.15 m²/g to about 2.2 m²/g, about 1.2 m²/g toabout 2.0 m²/g, about 1.25 m²/g to about 1.8 m²/g, about 1.3 m²/g toabout 1.6 m²/g, about 0.2 m²/g to less than 1.5 m²/g, about 0.4 m²/g toless than 1.5 m²/g, about 0.6 m²/g to less than 1.5 m²/g, about 0.8 m²/gto less than 1.5 m²/g, about 1.0 m²/g to less than 1.5 m²/g, or about1.1 m²/g to less than 1.5 m²/g.

Basis Weight

The basis weight, or grammage, is measured according to method number 3“Grammage” of Battery Council International Standard BCIS-03A (Rev Sep09) “BCI Recommended test Methods VRLA-AGM Battery Separators.” In someembodiments, the basis weight of the separator can be from about 0.25gsm (grams per square meter, or g/m²) to about 2500 gsm.

For example, in some embodiments, the basis weight is from about 1 gsmto about 1500 gsm, about 4 gsm to about 1000 gsm, about 15 gsm to about750 gsm, about 50 gsm to about 500 gsm, about 100 gsm to about 500 gsm,about 150 gsm to about 500 gsm, about 160 gsm to about 450 gsm, about180 gsm to about 400 gsm, about 200 gsm to about 350 gsm, about 220 gsmto about 320 gsm, about 240 gsm to about 300 gsm, about 250 gsm to about290 gsm, about 260 gsm to about 280 gsm, or about 270 gsm.

Thickness

The thickness is measured according to method number 12 “Thickness” ofBattery Council International Standard BCIS-03A (Rev Sep 09) “BCIRecommended test Methods VRLA-AGM Battery Separators.” This methodmeasures the thickness with a 1 square inch anvil load to a force of 20kPa. In some embodiments, the thickness of the separator can be fromabout 0.01 mm to about 15 mm. For example, in some embodiments thethickness of the separator is from about 0.05 mm to about 5 mm, about0.1 mm to about 3 mm, about 0.1 mm to about 3.5 mm, about 0.15 mm toabout 2 mm, about 0.15 mm to about 1.9 mm, about 0.15 mm to about 1.8mm, about 0.15 mm to about 1.7 mm, about 0.2 mm to about 2 mm, about 0.3mm to about 2 mm, about 0.4 mm to about 2 mm, about 0.5 mm to about 2mm, about 0.6 mm to about 2 mm, about 0.7 mm to about 2 mm, about 0.8 mmto about 2 mm, about 0.9 mm to about 2 mm, about 1 mm to about 2 mm,about 1.1 mm to about 2 mm, about 1.2 mm to about 2 mm, about 1.3 mm toabout 2 mm, about 1.1 mm to about 1.9 mm, about 1.2 mm to about 1.8 mmor about 1.3 mm to about 1.7 mm.

Density

The apparent density (referred to as “density” herein) of a separator ismeasured as the basis weight (grammage) of the separator in gsm (i.e.,g/m²) per unit thickness of the separator (e.g., in gsm/mm). In someembodiments, the density of the separator can be from about to about 75gsm/mm to about 400 gsm/mm. For example, in some embodiments the densityof the separator is from about 100 gsm/mm to about 350 gsm/mm, about 115gsm/mm to about 300 gsm/mm, about 125 gsm/mm to about 300 gsm/mm, about125 gsm/mm to about 250 gsm/mm, about 130 gsm/mm to about 240 gsm/mm,about 140 gsm/mm to about 225 gsm/mm, about 140 gsm/mm to about 210gsm/mm, about 140 gsm/mm to about 200 gsm/mm, about 150 gsm/mm to about220 gsm/mm, about 160 gsm/mm to about 220 gsm/mm, about 165 gsm/mm toabout 210 gsm/mm, about 170 gsm/mm to about 205 gsm/mm, about 175 gsm/mmto about 200 gsm/mm, greater than 180 gsm/mm to about 350 gsm/mm,greater than 180 gsm/mm to about 300 gsm/mm, greater than 180 gsm/mm toabout 300 gsm/mm, greater than 180 gsm/mm to about 250 gsm/mm, greaterthan 180 gsm/mm to about 240 gsm/mm, greater than 180 gsm/mm to about225 gsm/mm, greater than 180 gsm/mm to about 210 gsm/mm, or greater than180 gsm/mm to about 200 gsm/mm.

In some embodiments, the density of the separator is greater than 180gsm/mm. For example, in some embodiments, the density of the separatoris from greater than 180 gsm/mm to about 400 gsm/mm, greater than 180gsm/mm to about 350 gsm/mm, greater than 180 gsm/mm to about 300 gsm/mm,greater than 180 gsm/mm to about 250 gsm/mm, about 182 gsm/mm to about240 gsm/mm, about 182 gsm/mm to about 230 gsm/mm, about 182 gsm/mm toabout 220 gsm/mm, about 182 gsm/mm to about 200 gsm/mm, about 184 gsm/mmto about 240 gsm/mm, about 184 gsm/mm to about 230 gsm/mm, about 184gsm/mm to about 220 gsm/mm, about 184 gsm/mm to about 200 gsm/mm, about186 gsm/mm to about 240 gsm/mm, about 186 gsm/mm to about 230 gsm/mm,about 186 gsm/mm to about 220 gsm/mm, about 186 gsm/mm to about 200gsm/mm, about 188 gsm/mm to about 240 gsm/mm, about 188 gsm/mm to about230 gsm/mm, about 188 gsm/mm to about 220 gsm/mm, about 188 gsm/mm toabout 200 gsm/mm or about 185 gsm/mm to about 195 gsm/mm.

In some embodiments, a separator of the invention has the followingcharacteristics:

-   the mean pore size is less than 6 μm, about 0.5 μm to about 5.5 μm,    about 0.7 μm to about 5.3 μm, about 1.0 μm to about 5.0 μm, less    than 5 μm, about 1.0 μm to about 4.5 μm, about 1.2 μm to about 4.3    μm, about 1.5 μm to about 4.0 μm, less than 4 μm, about 1.5 μm to    about 3.9 μm, about 1.7 μm to about 3.9 μm, about 1.9 μm to about    3.9 μm about 2.1 μm to about 3.9 μm, about 2.3 μm to about 3.9 μm,    about 2.5 μm to about 3.9 μm, about 1.5 μm to about 3.8 μm, about    1.5 μm to about 3.7 μm, about 1.5 μm to about 3.6 μm, about 1.5 μm    to about 3.5 μm, about 1.7 μm to about 3.8 μm, about 1.9 μm to about    3.7 μm, about 2.1 μm to about 3.6 μm, about 2.3 μm to about 3.5 μm,    about 2.4 μm to about 3.4 μm, about 2.4 μm to about 3.0 μm or about    2.7 μm to about 3.3 μm;-   the basis weight is about 0.25 gsm to about 2500 gsm, about 1 gsm to    about 1500 gsm, about 4 gsm to about 1000 gsm, about 15 gsm to about    750 gsm, about 50 gsm to about 500 gsm, about 100 gsm to about 500    gsm, about 150 gsm to about 500 gsm, about 160 gsm to about 450 gsm,    about 180 gsm to about 400 gsm, about 200 gsm to about 350 gsm,    about 220 gsm to about 320 gsm, about 240 gsm to about 300 gsm,    about 250 gsm to about 290 gsm, about 260 gsm to about 280 gsm, or    about 270 gsm;-   the specific surface area is about 0.2 m²/g to about 2.5 m²/g, about    0.4 m²/g to about 2.5 m²/g, about 0.6 m²/g to about 2.5 m²/g, about    0.8 m²/g to about 2.5 m²/g, about 1.0 m²/g to about 2.5 m²/g, about    1.1 m²/g to about 2.5 m²/g, about 1.2 m²/g to about 2.5 m²/g, about    1.3 m²/g to about 2.5 m²/g, about 1.4 m²/g to about 2.5 m²/g, about    1.6 m²/g to about 2.5 m²/g, about 1.8 m²/g to about 2.5 m²/g, about    1.0 m²/g to about 2.4 m²/g, about 1.0 m²/g to about 2.2 m²/g, about    1.0 m²/g to about 2.0 m²/g, about 1.0 m²/g to about 1.8 m²/g, about    1.0 m²/g to about 1.6 m²/g, about 1.1 m²/g to about 2.4 m²/g, about    1.15 m²/g to about 2.2 m²/g, about 1.2 m²/g to about 2.0 m²/g, about    1.25 m²/g to about 1.8 m²/g, about 1.3 m²/g to about 1.6 m²/g, about    0.2 m²/g to less than 1.5 m²/g, about 0.4 m²/g to less than 1.5    m²/g, about 0.6 m²/g to less than 1.5 m²/g, about 0.8 m²/g to less    than 1.5 m²/g, about 1.0 m²/g to less than 1.5 m²/g, or about 1.1    m²/g to less than 1.5 m²/g; and-   the density is from greater than 180 gsm/mm to about 400 gsm/mm,    greater than 180 gsm/mm to about 350 gsm/mm, greater than 180 gsm/mm    to about 300 gsm/mm, greater than 180 gsm/mm to about 250 gsm/mm,    about 182 gsm/mm to about 240 gsm/mm, about 182 gsm/mm to about 230    gsm/mm, about 182 gsm/mm to about 220 gsm/mm, about 182 gsm/mm to    about 200 gsm/mm, about 184 gsm/mm to about 240 gsm/mm, about 184    gsm/mm to about 230 gsm/mm, about 184 gsm/mm to about 220 gsm/mm,    about 184 gsm/mm to about 200 gsm/mm, about 186 gsm/mm to about 240    gsm/mm, about 186 gsm/mm to about 230 gsm/mm, about 186 gsm/mm to    about 220 gsm/mm, about 186 gsm/mm to about 200 gsm/mm, about 188    gsm/mm to about 240 gsm/mm, about 188 gsm/mm to about 230 gsm/mm,    about 188 gsm/mm to about 220 gsm/mm, about 188 gsm/mm to about 200    gsm/mm or about 185 gsm/mm to about 195 gsm/mm.

In some embodiments, a separator of the invention has the followingcharacteristics:

-   the mean pore size is less than 6 μm, about 0.5 μm to about 5.5 μm,    about 0.7 μm to about 5.3 μm, about 1.0 μm to about 5.0 μm, less    than 5 μm, about 1.0 μm to about 4.5 μm, about 1.2 μm to about 4.3    μm, about 1.5 μm to about 4.0 μm, less than 4 μm, about 1.5 μm to    about 3.9 μm, about 1.7 μm to about 3.9 μm, about 1.9 μm to about    3.9 μm about 2.1 μm to about 3.9 μm, about 2.3 μm to about 3.9 μm,    about 2.5 μm to about 3.9 μm, about 1.5 μm to about 3.8 μm, about    1.5 μm to about 3.7 μm, about 1.5 μm to about 3.6 μm, about 1.5 μm    to about 3.5 μm, about 1.7 μm to about 3.8 μm, about 1.9 μm to about    3.7 μm, about 2.1 μm to about 3.6 μm, about 2.3 μm to about 3.5 μm,    about 2.4 μm to about 3.4 μm, about 2.4 μm to about 3.0 μm or about    2.7 μm to about 3.3 μm;-   the basis weight is about 0.25 gsm to about 2500 gsm, about 1 gsm to    about 1500 gsm, about 4 gsm to about 1000 gsm, about 15 gsm to about    750 gsm, about 50 gsm to about 500 gsm, about 100 gsm to about 500    gsm, about 150 gsm to about 500 gsm, about 160 gsm to about 450 gsm,    about 180 gsm to about 400 gsm, about 200 gsm to about 350 gsm,    about 220 gsm to about 320 gsm, about 240 gsm to about 300 gsm,    about 250 gsm to about 290 gsm, about 260 gsm to about 280 gsm, or    about 270 gsm;-   the specific surface area of the separator is less than 1.5 m²/g,    about 0.1 m²/g to less than 1.5 m²/g, about 0.2 m²/g to less than    1.5 m²/g, about 0.3 m²/g to less than 1.5 m²/g, about 0.4 m²/g to    less than 1.5 m²/g, about 0.5 m²/g to less than 1.5 m²/g, about 0.6    m²/g to less than 1.5 m²/g, about 0.7 m²/g to less than 1.5 m²/g,    about 0.8 m²/g to less than 1.5 m²/g, about 0.9 m²/g to less than    1.5 m²/g, about 1.0 m²/g to less than 1.5 m²/g, about 1.1 m²/g to    less than 1.5 m²/g, about 1.2 m²/g to less than 1.5 m²/g, about 1.3    m²/g to less than 1.5 m²/g, about 1.4 m²/g to less than 1.5 m²/g,    about 1.0 m²/g to about 1.45 m²/g, about 1.0 m²/g to about 1.4 m²/g,    about 1.0 m²/g to about 1.35 m²/g, about 1.0 m²/g to about 1.3 m²/g,    about 1.1 m²/g to about 1.45 m²/g, about 1.15 m²/g to about 1.45    m²/g, about 1.2 m²/g to about 1.45 m²/g, about 1.25 m²/g to about    1.45 m²/g or about 1.3 m²/g to about 1.45 m²/g; and-   the density is about 75 gsm/mm to about 400 gsm/mm, about 100 gsm/mm    to about 350 gsm/mm, about 115 gsm/mm to about 300 gsm/mm, about 125    gsm/mm to about 300 gsm/mm, about 125 gsm/mm to about 250 gsm/mm,    about 130 gsm/mm to about 240 gsm/mm, about 140 gsm/mm to about 225    gsm/mm, about 140 gsm/mm to about 210 gsm/mm, about 140 gsm/mm to    about 200 gsm/mm, about 150 gsm/mm to about 220 gsm/mm, about 160    gsm/mm to about 220 gsm/mm, about 165 gsm/mm to about 210 gsm/mm,    about 170 gsm/mm to about 205 gsm/mm, about 175 gsm/mm to about 200    gsm/mm, greater than 180 gsm/mm to about 350 gsm/mm, greater than    180 gsm/mm to about 300 gsm/mm, greater than 180 gsm/mm to about 300    gsm/mm, greater than 180 gsm/mm to about 250 gsm/mm, greater than    180 gsm/mm to about 240 gsm/mm, greater than 180 gsm/mm to about 225    gsm/mm, greater than 180 gsm/mm to about 210 gsm/mm, or greater than    180 gsm/mm to about 200 gsm/mm.

Compressibility

Compressibility of a separator is measured according to Battery CouncilInternational Battery Technical Manual BCIS-03A (Rev. Sep 09) methodnumber 1, “Compressibility and Recovery of Recombinant Battery SeparatorMaterial”, and converted to % change in thickness of the separator(thickness measured before and after compression test). Thecompressibility of a separator can be expressed as percent compression,specifically, as the percent change in thickness of the separator ongoing from 10 kPa to 100 kPa (i.e., percent compression=((T@10 kPa−T@100kPa)/T@10 kPa)*100, where T is the thickness at the indicated pressure).In some embodiments, the percent compression (dry) of the separator canbe less than 31%. For example, in some embodiments the percentcompression (dry) of the separator is less than 30%, less than 29%,about 20% to 31%, about 20% to about 30%, about 20% to about 29%, about23% to 31%, about 23% to about 30%, about 23% to about 29%, about 25% to31%, about 25% to about 30%, about 25% to about 29%, about 26% to 31%,about 26% to about 30% or about 26% to about 29%.

The compressibility of a separator can be also expressed as percentrecovery, specifically, on going from 10 kPa to 100 kPa and back to 10kPa as the percent retention of thickness at 20 kPa on the recoverycycle compared to the thickness at 20 kPa on the compression cycle(i.e., percent recovery=(T_(rec)/T_(comp))*100, where T_(comp) is thethickness at 20 kPa on the compression cycle and T_(rec) is thethickness at 20 kPa on the recovery cycle). In some embodiments, thepercent recovery (dry) of the separator can be greater than 84%. Forexample, in some embodiments, the percent recovery (dry) of theseparator is greater than 85%, greater than 86%, greater than 87%, about84% to about 90%, about 85% to about 90%, about 86% to about 90%, about87% to about 90%, about 84% to about 88%, about 85% to about 88% orabout 86% to about 88%.

Measurements of percent compression and percent recovery for exemplaryseparators of the invention compared with reference separators arepresented in Example 2.5.

Tensile Strength

Tensile strength of a separator is measured according to Battery CouncilInternational Battery Technical Manual BCIS-03A (Rev. Sep 09), methodnumber 9, “Tensile Elongation & Strength”. In some embodiments, thetensile strength (machine direction, MD) of the separator can be about0.01 kN/m to about 50 kN/m. In some embodiments, the tensile strength(cross direction, CD) of the separator can be about 0.01 kN/m to about25 kN/m.

For example, in some embodiments the tensile strength (MD) of theseparator is about 0.01 kN/m to about 30 kN/m, about 0.01 kN/m to about15 kN/m, about 0.01 kN/m to about 10 kN/m, about 0.01 kN/m to about 5kN/m, about 0.01 kN/m to about 4 kN/m, about 0.01 kN/m to about 3 kN/m,about 0.01 kN/m to about 2 kN/m, about 0.1 kN/m to about 15 kN/m, about0.1 kN/m to about 10 kN/m, about 0.1 kN/m to about 5 kN/m, about 0.1kN/m to about 4 kN/m, about 0.1 kN/m to about 3 kN/m, about 0.1 kN/m toabout 2 kN/m, about 0.17 kN/m to about 10 kN/m, about 0.17 kN/m to about5 kN/m, about 0.17 kN/m to about 4 kN/m, about 0.17 kN/m to about 3kN/m, about 0.17 kN/m to about 2 kN/m, about 0.3 kN/m to about 10 kN/m,about 0.3 kN/m to about 5 kN/m, about 0.3 kN/m to about 4 kN/m, about0.3 kN/m to about 3 kN/m or about 0.3 kN/m to about 2 kN/m.

For example, in some embodiments the tensile strength (CD) of theseparator is about 0.01 kN/m to about 15 kN/m, about 0.01 kN/m to about7.5 kN/m, about 0.01 kN/m to about 5 kN/m, about 0.01 kN/m to about 2.5kN/m, about 0.01 kN/m to about 2 kN/m, about 0.01 kN/m to about 1.5kN/m, about 0.01 kN/m to about 1 kN/m, about 0.05 kN/m to about 7.5kN/m, about 0.05 kN/m to about 5 kN/m, about 0.05 kN/m to about 2.5kN/m, about 0.05 kN/m to about 2 kN/m, about 0.05 kN/m to about 1.5kN/m, about 0.05 kN/m to about 1 kN/m, about 0.1 kN/m to about 5 kN/m,about 0.1 kN/m to about 2.5 kN/m, about 0.1 kN/m to about 2 kN/m, about0.1 kN/m to about 1.5 kN/m, about 0.1 kN/m to about 1 kN/m, about 0.15kN/m to about 5 kN/m, about 0.15 kN/m to about 2.5 kN/m, about 0.15 kN/mto about 2 kN/m, about 0.15 kN/m to about 1.5 kN/m or about 0.15 kN/m toabout 1 kN/m.

Wet Tensile Strength

Wet tensile strength of a separator is measured according to theprocedure described in Example 2.2. In some embodiments, the wet tensilestrength (machine direction, MD) of the separator can be about 0.01 kN/mto about 20 kN/m. In some embodiments, the wet tensile strength (crossdirection, CD) of the separator can be about 0.01 kN/m to about 10 kN/m.

For example, in some embodiments the wet tensile strength (MD) of theseparator is about 0.01 kN/m to about 15 kN/m, about 0.01 kN/m to about10 kN/m, about 0.01 kN/m to about 5 kN/m, about 0.01 kN/m to about 4kN/m, about 0.01 kN/m to about 3 kN/m, about 0.01 kN/m to about 2 kN/m,about 0.01 kN/m to about 1 kN/m, about 0.05 kN/m to about 10 kN/m, about0.05 kN/m to about 5 kN/m, about 0.05 kN/m to about 4 kN/m, about 0.05kN/m to about 3 kN/m, about 0.05 kN/m to about 2 kN/m, about 0.05 kN/mto about 1 kN/m, about 0.1 kN/m to about 5 kN/m, about 0.1 kN/m to about4 kN/m, about 0.1 kN/m to about 3 kN/m, about 0.1 kN/m to about 2 kN/mor about 0.1 kN/m to about 1 kN/m.

For example, in some embodiments the wet tensile strength (CD) of theseparator is about 0.01 kN/m to about 5 kN/m, about 0.01 kN/m to about 4kN/m, about 0.01 kN/m to about 3 kN/m, about 0.01 kN/m to about 2 kN/m,about 0.01 kN/m to about 1 kN/m, about 0.01 kN/m to about 0.5 kN/m,about 0.03 kN/m to about 3 kN/m, about 0.03 kN/m to about 2 kN/m, about0.03 kN/m to about 1.5 kN/m, about 0.03 kN/m to about 1 kN/m, about 0.05kN/m to about 2.5 kN/m, about 0.05 kN/m to about 2 kN/m, about 0.05 kN/mto about 1.5 kN/m, about 0.05 kN/m to about 1 kN/m or about 0.05 kN/m toabout 0.5 kN/m.

Vacuum Fill (Acid Filling) Time

Vacuum fill (acid filling) time of a separator is measured according tothe procedure described in Example 2.3. In some embodiments, theseparator can exhibit a vacuum fill time of about 50 sec to about 500sec.

For example, in some embodiments the separator exhibits a vacuum filltime of about 75 sec to about 450 sec, about 100 sec to about 400 sec,about 115 sec to about 360 sec, about 130 sec to about 310 sec, about145 sec to about 295 sec or about 160 sec to about 280 sec.

Making a Separator

A separator of the invention can be produced using a wet laid or a drylaid process. In general, a wet laid process involves mixing togetherthe fibers; for example, glass fibers (e.g., chopped strand and/ormicroglass) may be mixed together, optionally with any synthetic fibers,to provide a glass fiber slurry. In some cases, the slurry is anaqueous-based slurry. In certain embodiments, the microglass fibers, andoptionally any chopped strand and/or synthetic fibers, are storedseparately in various holding tanks prior to being mixed together. Thesefibers may be processed through a pulper before being mixed together. Insome embodiments, combinations of chopped strand glass fibers,microglass fibers, and/or synthetic fibers are processed through apulper and/or a holding tank prior to being mixed together. As discussedabove, microglass fibers may include fine microglass fibers and coarsemicroglass fibers.

It should be appreciated that any suitable method for creating a glassfiber slurry may be used. In some cases, additional additives are addedto the slurry to facilitate processing. The temperature may also beadjusted to a suitable range, for example, between 33° F. (0.5° C.) and100° F. (38° C.), (e.g., between 50° F. (10° C.) and 85° F. (29° C.)).In some embodiments, the temperature of the slurry is maintained. Insome cases, the temperature is not actively adjusted.

In some embodiments, the wet laid process uses similar equipment as aconventional papermaking process, which includes a hydropulper, a formeror a headbox, a dryer, and an optional converter. For example, theslurry may be prepared in one or more pulpers. After appropriatelymixing the slurry in a pulper, the slurry may be pumped into a headbox,where the slurry may or may not be combined with other slurries oradditives may or may not be added. The slurry may also be diluted withadditional water such that the final concentration of fiber is in asuitable range, such as for example, between about 0.1% to 1.5% byweight.

In some cases, the pH of the glass fiber slurry may be adjusted asdesired. For instance, the pH of the glass fiber slurry may rangebetween about 1.5 and about 4.5, or between about 2.6 and about 3.2.

Before the slurry is sent to a headbox, the slurry may be passed throughcentrifugal cleaners for removing unfiberized glass or shot. The slurrymay or may not be passed through additional equipment such as refinersor deflakers to further enhance the dispersion of the fibers. Fibers maythen be collected on a screen or wire at an appropriate rate using anysuitable machine, e.g., a fourdrinier, a rotoformer, a cylinder, aninclined wire fourdrinier, a gap former, a twin wire, a multiply former,a pressure former, a top former, etc.).

In some embodiments, the process involves introducing binder (and/orother components) into a pre-formed glass fiber layer. In someembodiments, as the glass fiber layer is passed along an appropriatescreen or wire, different components included in the binder, which maybe in the form of separate emulsions, are added to the glass fiber layerusing a suitable technique. In some cases, each component of the binderresin is mixed as an emulsion prior to being combined with the othercomponents and/or glass fiber layer. In some embodiments, the componentsincluded in the binder may be pulled through the glass fiber layerusing, for example, gravity and/or vacuum. In some embodiments, one ormore of the components included in the binder resin may be diluted withsoftened water and pumped into the glass fiber layer.

In other embodiments, a dry laid process is used. In a dry laid process,glass fibers are dispersed in air that is blown onto a conveyor, andoptionally a binder is then applied. Dry laid processing is typicallymore suitable for the production of highly porous media includingbundles of glass fibers.

Any method of densification of the separator can be employed at theappropriate stage in the process to obtain a separator having thedesired characteristic (for example, pore size).

For example, in some embodiments, during the sheet forming process, aswater is being drained from the stock slurry, the fibers can be drawntightly together to densify the web through the use of vacuum applied byvarious elements of the papermachine forming section. These elements mayinclude, papermachine table rolls, vacuum assisted or non-vacuumassisted hydrofoils, flatboxes, suction boxes, vacuum couch rolls,and/or other de-watering equipment commonly used in the paper industry.The amount of water to be drained may be variable depending on the levelof densification desired in the end product. Vacuum imparted by thisequipment may range between 0.5″ and 30″ of mercury. The use of apressure forming head box may be employed to exert pressure on the stockslurry to assist with drainage and densification of the web beingproduced.

In some embodiments, the separator web being produced is physicallypressed to effect densification.

In some embodiments, the pressing step occurs after the web is formedand has enough integrity to leave the forming section of thepapermachine, passing between and being compressed by 2 press rollsprior to entering the dryer section. The press rolls may be unfelted orfelted, to aid in water removal. Additionally, the rolls may becontrolled at a fixed or unfixed gap setting.

In some embodiments, the pressing step is performed by a press rollwhile the sheet is still supported on the forming fabric, optionallyover a vacuum element to assist water removal expelled by the pressingaction. The pressing step may also be performed by a press rollpositioned over a vacuum couch roll.

In some embodiments, pressing is achieved on the forming section of thepapermachine through the use of a dandy roll where the sheet issupported by the forming fabric.

In some embodiments, pressing is achieved by a top wire dewateringsystem positioned above the forming fabric.

Each of the foregoing forms of pressure may employ fixed gap, unfixedgap, weight of the roll or equipment, pressure or force applied, drivenor un-driven, use of vacuum or non-vacuum water removal.

The use of thickness measurement equipment may be used as part of aprocess control loop to provide feedback information to the pressingequipment to control the densification of the web being produced. Thethickness measurement may be performed continuously as a part of theprocess control scanning equipment commonly used throughout the paperindustry. The equipment may employ sensors that physically make contactwith the web to detect web thickness. The thickness detection may alsobe made using laser measurement systems. The thickness detection devicesmay be held stationary over the web or may oscillate back and forthacross the entire width of the web as it is produced. These systems mayalso be employed while the web is in the wet state before entering thedrying process and/or after the web has been dried and prior to thepapermachine reel section.

Any number of intermediate processes (e.g., calendering, laminating,etc.) and addition of additives may be utilized throughout the separatorformation process. Additives can also be added either to the slurry orto the separator as it is being formed, including but not limited to,salts, fillers including silica, binders, and latex. In someembodiments, the additives may comprise between about 0% to about 30% byweight of the separator. Furthermore, the drying temperature may vary,also depending on the fiber composition. In various embodiments, thedrying temperature may range from approximately 100° C. to approximately700° C. The separator may comprise more than one layer, each layeroptionally comprising different types of fibers with different physicaland chemical characteristics.

Batteries

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and any battery separator describedherein.

Thus, in one aspect, the invention relates to a lead-acid batterycomprising a negative plate, a positive plate, and a battery separatordisposed between the negative and positive plates, wherein the batteryseparator comprises glass fibers and has a basis weight (gsm), aspecific surface area (m²/g), a density (gsm/mm) and a mean pore size(μm), wherein the following equation (including the provisos, “eq. 1”)is satisfied (when the quantities have the indicated units):

${{mean}\mspace{14mu} {pore}\mspace{14mu} {size}} < {\left( \frac{270}{{basis}\mspace{14mu} {weight}} \right)^{0.53}*\frac{1.6}{{specific}\mspace{14mu} {surface}\mspace{14mu} {area}}*\left( {\frac{65}{\sqrt{density}} - 1.8} \right)}$

provided that:

the specific surface area is less than 1.5 m²/g, or

the density is greater than 180 gsm/mm.

The use of pasting paper in construction of lead-acid batteries is wellknown in the art. Pasting paper helps retain the active material pastein proximity to the grid prior to curing. However, the majority ofpasting paper remains on the surface of the plate in contact with theseparator, and therefore affects certain characteristics. In someembodiments, the present invention encompasses the insight that theratio of the specific surface area of the pasting paper to the specificsurface area of the separator affects certain properties such as acidfilling time. The relationship between acid fill time and the ratio ofspecific surface area of pasting paper to separator is illustrated inFIG. 4 for two exemplary separators of the invention and one referenceseparator. In some embodiments, the invention relates to a lead-acidbattery comprising a negative plate; a positive plate; a batteryseparator disposed between the negative and positive plates, wherein thebattery separator comprises glass fibers and satisfies eq. 1; andpasting paper disposed between the battery separator and the negativeand/or positive plate(s), wherein the ratio of the specific surface areaof the pasting paper to the specific surface area of the separator isabout 1.0 or less. For example, in some embodiments the ratio of thespecific surface area of the pasting paper to the specific surface areaof the separator is about 0.5 to about 1.0, about 0.6 to about 1.0,about 0.7 to about 1.0 or about 0.8 to about 1.0.

It is to be understood that the other components of the battery that arenot explicitly discussed herein can be conventional battery components.Positive plates and negative plates can be formed of conventional leadacid battery plate materials. For example, in container formattedbatteries, plates can include grids that include a conductive material,which can include, but is not limited to, lead, lead alloys, graphite,carbon, carbon foam, titanium, ceramics (such as Ebonex®), laminates andcomposite materials. The grids are typically pasted with activematerials. The pasted grids are typically converted to positive andnegative battery plates by a process called “formation.” Formationinvolves passing an electric current through an assembly of alternatingpositive and negative plates with separators between adjacent plateswhile the assembly is in a suitable electrolyte.

As a specific example, positive plates contain lead as the activematerial, and negative plates contain lead dioxide as the activematerial. Plates can also contain one or more reinforcing materials,such as chopped organic fibers (e.g., having an average length of 0.125inch or more), chopped glass fibers, metal sulfate(s) (e.g., nickelsulfate, copper sulfate), red lead (e.g., a Pb₃O₄-containing material),litharge, paraffin oil, and/or expander(s). In some embodiments, anexpander contains barium sulfate, carbon black and lignin sulfonate asthe primary components. The components of the expander(s) can bepre-mixed or not pre-mixed. Expanders are commercially available from,for example, Hammond Lead Products (Hammond, Ind.) and Atomized ProductsGroup, Inc. (Garland, Tex.). An example of a commercially availableexpander is Texex® expander (Atomized Products Group, Inc.). In certainembodiments, the expander(s), metal sulfate(s) and/or paraffin arepresent in negative plates, but not positive plates. In someembodiments, positive plates and/or negative plates contain fibrousmaterial or other glass compositions.

A battery can be assembled using any desired technique. For example,separators are wrapped around plates (e.g., cathode plates, anodeplates). Positive plates, negative plates and separators are thenassembled in a case using conventional lead acid battery assemblymethods. In certain embodiments, separators are compressed before theyare assembled in the case. In certain embodiments, separators arecompressed after they are assembled in the case. An electrolytic mixtureis then dispensed into the case.

In some embodiments, the electrolyte is sulfuric acid. In someembodiments, the specific gravity of the sulfuric acid is between 1.21and 1.32, or between 1.28 and 1.31. In certain embodiments the specificgravity of the sulfuric acid is 1.26. In certain embodiments thespecific gravity of the sulfuric acid is about 1.3.

EXAMPLES Example 1 Separator Composition

In each of the separators described below, one or more of the followingfibers are employed:

Designation Surface Area Diameter Fiber 1  2.1 m²/g 0.8 μm Fiber 2 1.45m²/g 1.4 μm Fiber 3 0.62 m²/g 2.6 μm Fiber 4  0.1 m²/g  14 μm

Example 1.A Reference Separator 1: of 60% Fiber 1/40% Fiber 3

Fiber 1 was added to a hydropulper containing water and sulfuric acid toform a fiber dispersion slurry. The pH was maintained at 2.7. The fiberslurry was stored in a chest (tank) under agitation. The same processwas repeated for Fiber 3, and the fiber slurry thus prepared was storedin a second chest under agitation. The two chests supplied the slurriesto the headbox of a paper machine (Fourdrinier). The flow rates of therespective slurries were set so that the dry weights of the fiberscorresponded to 60% Fiber 1 and 40% Fiber 3. The fiber slurries weremixed within the head box creating a uniform fiber slurry whichcontacted a wire of the forming zone. The slurry was then dewateredusing vacuum. The separator was then dried using steam heated driercans. The separator was collected at the other end of the machine assheets.

Example 1.B Reference Separator 2: of 89% Fiber 2/11% Fiber 4

Using a procedure similar to that for Example 1.A, a single slurry chestwas prepared using Fiber 2 and Fiber 4 at a weight ratio of 89% Fiber 2to 11% Fiber 4. The chest supplied the slurry to the headbox of a papermachine (Fourdrinier), and sheets were made in the same manner as inExample 1.A.

Example 1.1 Separator 1: of 24% Fiber 1/61% Fiber 2/10% Fiber 3/5% Fiber4

Using a procedure similar to that for Example 1.A, three chests ofslurries were prepared. One contained 95% Fiber 1 and 5% Fiber 4, thesecond contained 95% Fiber 2 and 5% Fiber 4, and the third contained 95%Fiber 3 and 5% Fiber 4. These fibers slurries were supplied to the headbox with the respective flows set to result in 24% Fiber 1, 61% Fiber 2,10% Fiber 3, and 5% Fiber 4. After vacuum dewatering, but before drying,the web is passed through a wet press station which consists of anadjustable gap between a hard roll and a forming fabric. The density ofthe dry sheet is determined by measuring grammage and thickness, and theadjustable gap of the wet press is changed, either wider or narrower asneeded, which changes the density of the resulting dry sheet. The gapwas adjusted until the desired density target of 190 gsm/mm was met.Then the gap was set and the sheets were made in the same manner as inExample 1.A.

Example 1.2 Separator 2: of 24% Fiber 1/45% Fiber 2/26% Fiber 3/5% Fiber4

Using the chests of slurries prepared for Example 1.1, the respectiveflow rates of the slurries were set to result in a combined dry weightof 24% Fiber 1, 45% Fiber 2, 26% Fiber 3, and 5% Fiber 4. The density ofthe separator was adjusted and sheets were made in the same manner as inExample 1.1.

Example 2 Separator Characteristics Example 2.1

The following characteristics were determined for the separators ofExample 1.

Characteristic Reference 1 Reference 2 Separator 1 Separator 2 basisweight 278 260. 277 275 (g/m²) thickness @ 1.63 1.49 1.46 1.45 20 kPa(mm) density @ 171 175 190. 190. 20 kPa (gsm/mm) mean pore size 3.094.00 3.28 2.69 (μm) wet tensile 0.29 0.095 0.20 0.13 strength, MD (kN/m)surface area 1.51 1.30 1.46 1.32 (m²/g)

Example 2.2 Measurement of Wet Tensile Strength

Wet tensile strength of a separator can be measured according to thefollowing procedure.

Equipment

-   Instron® Series 9 tensiometer (Norwood, Mass.)-   Water Container-   Stand Assembly with Clip for Hanging Sample

Sample Preparation

-   1. Wrap a length of polythene around the lower jaw mechanism of the    tensiometer and seal with adhesive tape. (Ensure that lower    mechanism is fully waterproofed.)-   2. Wrap a length of absorbent sheet around the base of the    tensiometer. (Ensure that excess water is captured or contained.)-   3. Ensure the distance between the jaws is set at 100 mm.-   4. Set up the “Wet tensile” (50×100 mm) test from the software menu.-   5. Part-fill a shallow container with deionized water and set up a    stand to hang a sample over it. (Container must completely    accommodate a 200 mm-length sample.)-   6. Cut a 150×50 mm sample in the machine- or cross-direction.

Sample Testing

-   7. Ensure the sample is identified as MD (machine direction) or CD    (cross direction).-   8. Immerse the sample completely in the deionized water for 1    minute.-   9. Remove the sample and hang, allowing excess water to drip off,    for 30 seconds.-   10. Place the sample in the tensiometer and run a tensile test.-   11. Record tensile strength (kN/m).

Example 2.3 Measurement of Vacuum Fill (Acid Filling) Time

Vacuum fill (acid filling) time of a separator can be measured accordingto the following procedure. Measurements of acid filling time were madefor Reference separator 1 and Example Separators 1 and 2:

Reference 1 220 sec Example 1 250 sec Example 2 178 sec

Equipment

-   1.26 s.g. (specific gravity) sulfuric acid-   Sample(s) to be tested-   8″×1.9375″ sample strip-   12″×6″×1″ Perspex blocks, with holes drilled for attaching and    inlet/outlet barbs for acid filling-   Screw-thread, nuts and washers-   Shims, various thicknesses, for the required gap-   Rubber gasket or O-ring cord for ‘sealing’ the sample-   Acid feed assembly (Glassware with tubing), including stand and    clamps-   Vacuum pump-   Timer/stopwatch

Sample Preparation

-   1. Measure the grammage of the separator, to one decimal point, in    g/m² (W).-   2. Calculate the required thickness for each density value:    -   2.1. Thickness=grammage÷compressed density (typically 220        gsm/mm).-   3. Determine the shims and o-ring cords required for each thickness    calculated:    -   3.1. Shims should be to the nearest available thickness        increment.    -   3.2. O-ring cord diameter should be equal to, or greater than,        the shim thickness, but no more than 0.5 mm greater.-   4. Cut the sample 8″×1.9375″ in the machine direction.-   5. Weigh the sample to determine the amount of acid needed.-   6. Put the bolts through the Perspex base and lay the assembly on    the bench.-   7. Place the sample on the Perspex base in between the grooves on    the plate.-   8. Align the rubber gasket on the edges of the separator in the    grooves on the plate.-   9. Put the required shims onto each bolt.-   10. Add the Perspex face to the top of this assembly and    finger-tighten the nuts.-   11. Tighten the nuts using the torque wrench (set at 10 N).    -   (refer to FIG. 1.)

Sample Testing

-   12. Connect vacuum pump to the outlet barb.-   13. Stand the block upright and plug in the acid feed assembly.-   14. Add the appropriate amount of acid to the top of the feed    system. Make sure the valve is closed.-   15. Turn the vacuum pump on and allow system to come to equilibrium    at 500 mm Hg.-   16. When the system has come to equilibrium at 500 mm Hg, open up    the valve to the acid and record the acid front travel time required    to complete filling of the sample.

Example 2.4 Measurement of Acid Stratification Distance

This Method is Used to Determine the Degree to which Sulfuric AcidDisplaces Water in a glass-mat separator while under compression. Themeasured stratification distance can provide an indication of potentialstratification within a battery cell, a phenomenon in which the specificgravity of the electrolyte (acid) varies throughout the height of thecell.

Equipment

-   Methyl red, diluted in 1.28 s.g. (specific gravity) sulfuric acid    (1:100 dilution)-   1.1 s.g. (specific gravity) sulfuric acid-   Sample(s) to be tested-   300×150×50 mm Perspex blocks, with holes drilled for attaching-   Screw-thread, nuts and washers-   Shims, various thicknesses, for the required gap-   Rubber gasket or O-ring cord, various diameters, for ‘sealing’ the    sample-   Pyrex dish to hold block assembly and acid

Sample Preparation

-   1. Measure the grammage of the separator, to one decimal point, in    g/m² (W).-   2. Measurements of acid stratification distance are typically made    at about 200 g/m²/mm compressed density and/or about 240 g/m²/mm    compressed density.-   3. Calculate the required thickness for each density value:    -   3.1. Thickness=grammage÷compressed density (either 200 or 240).-   4. Determine the shims and o-ring cords required for each thickness    calculated:    -   4.1. Shims should be to the nearest available thickness        increment.    -   4.2. O-ring cord diameter should be equal to, or greater than,        the shim thickness, but no more than 0.5 mm greater.-   5. Cut two samples of separator, 250×50 mm, in the machine    direction.-   6. Immerse the sample in 1.1 s.g. acid for one minute.-   7. Put the bolts through the Perspex base and lay the assembly on    the bench.-   8. Place wet sample on the Perspex base.-   9. Align the o-ring cords tight to the edges of the separator.-   10. Put the required shims onto each bolt.-   11. Add the Perspex face to the top of this assembly and    finger-tighten the nuts.-   12. Push the o-ring cords tightly to the sample edge all along the    AGM, particularly at the top.-   13. Tighten the nuts using the torque wrench (set at 10 Nm/88.5    in/lbf).    -   (refer to FIG. 3.)

Sample Testing

-   14. Put the full block in an empty Pyrex dish with a 20 mm 1.1 s.g.    acid level.-   15. Add dyed sulfuric acid (1.28 s.g.) into the space at the top of    the sample and start the timer (60-minute countdown).-   16. The acid will travel or diffuse through the pores of the    separator and a visual red/pink ‘tide mark’ will be observed,    displaying the magnitude of displacement.-   17. Check the status of the displacement at regular intervals (every    15 minutes is sufficient).-   18. After the 60 minutes is completed, measure the total acid    displacement (distance from the top of the sample to the red/pink    mark).-   19. Report acid stratification distance, at each density measured in    mm.

Example 2.5 Measurement of Compressibility

Percent compression and percent recovery of exemplary Separators 1 and 2and Reference separators 1 and 2 were measured as described above under“Compressibility”, with reference to BCIS-03A (Rev. Sep09) methodnumber 1. Results are shown in FIG. 2 and in the table below.

Percent compression Percent recovery Separator (10 kPa to 100 kPa) (20kPa) Reference 1 39.4 77 Reference 2 31.8 83.1 Separator 1 26.6 87.5Separator 2 28.6 87.5

1. A battery separator comprising fibers, wherein the fibers comprise atleast 5% glass fibers, and having a basis weight (in gsm), a specificsurface area (in m²/g), a density (in gsm/mm) and a mean pore size (inμm), wherein the following equation is satisfied:${{mean}\mspace{14mu} {pore}\mspace{14mu} {size}} < {\left( \frac{270}{{basis}\mspace{14mu} {weight}} \right)^{0.53}*\frac{1.6}{{specific}\mspace{14mu} {surface}\mspace{14mu} {area}}*\left( {\frac{65}{\sqrt{density}} - 1.8} \right)}$provided that: the specific surface area is less than 1.50 m²/g; or thedensity is greater than 180 gsm/mm.
 2. The battery separator of claim 1,wherein the specific surface area is less than 1.50 m²/g.
 3. The batteryseparator of claim 1, wherein the density is greater than 180 gsm/mm. 4.The battery separator of claim 1, wherein the fibers comprise about 5%to about 50% fibers having an average diameter less than or equal to 1.0μm.
 5. The battery separator of claim 4, wherein the fibers compriseabout 15% to about 35% fibers having an average diameter less than orequal to 1.0 μm.
 6. The battery separator of claim 1, wherein the meanpore size is less than 6 μm.
 7. The battery separator of claim 6,wherein the mean pore size is less than 5 μm.
 8. The battery separatorof claim 6, wherein the mean pore size is less than 4 μm.
 9. The batteryseparator of claim 1, wherein the density is about 75 gsm/mm to about400 gsm/mm.
 10. The battery separator of claim 9, wherein the density isabout 160 gsm/mm to about 220 gsm/mm.
 11. The battery separator of claim1, wherein the wet tensile strength (MD) of the separator is about 0.01kN/m to about 20 kN/m.
 12. The battery separator of claim 11, whereinthe wet tensile strength (MD) of the separator is about 0.1 kN/m toabout 3 kN/m.
 13. The battery separator of claim 1, wherein the wettensile strength (CD) of the separator is about 0.01 kN/m to about 10kN/m.
 14. The battery separator of claim 13, wherein the wet tensilestrength (CD) of the separator is about 0.05 kN/m to about 1.5 kN/m. 15.The battery separator of claim 1, wherein the percent compression isless than 31%.
 16. The battery separator of claim 1, wherein the percentrecovery is greater than 84%.